1. Field of the Invention
This invention provides a metamaterial substrate which may be integrated with electronic circuit components and/or employed as a circuit layer in Printed Circuit Board and Wiring Board (collectively, “PCBs”) capable of transmitting, receiving and reflecting electromagnetic energy, altering electromagnetic properties of natural circuit materials, enhancing electrical characteristics of electronic components (such as filters, antennas, baluns, power dividers, transmission lines, amplifiers, power regulators, and printed circuit elements) in systems and sub-systems circuit designs.
2. Related Art
Metamaterials are realized by repeating a basic building block in a specific periodic pattern. The basic building block is known as the Unit Element (“UE”), and it defines the fundamental properties of the metamaterial. Several different designs are possible for UE. For example, one UE is the Sievenpiper mushroom UE, as shown in FIG. 1. The top conductive patch 100 may be connected to the bottom ground plane 102 by a shorting post 104 also known as a via. This configuration can be shown in FIG. 2 where the dielectric material 200 forms a support structure for conductive patches 202 with the bottom ground plane 204. The top conductive patches 202 may be connected to the bottom ground plane 204 by a shorting post 206 also known as a via. Sievenpiper also indicates that when there is a thin structure in the mushroom UE, the bandwidth is also reduced.
FIG. 3 is a prior art perspective view of a mushroom UE having a top conductive patch 300, a via 302, a dielectric substrate 304 and a ground plane 306. FIG. 4 is a simplified electrical model illustrating a left-handed shunt inductance LL and left-handed series capacitance CL created by the shorting post 104 or 206 and the gap between each mushroom UE 100 or 202, respectively. The shorting post 104 or 206 provides the inductance LL which at least in part creates the Electromagnetic Band Gap (“EBG”) ground plane or surface. However, an ideal metamaterial mushroom UE cannot be practically/physically realized due to parasitic effects. Likewise, FIG. 5 depicts a general model comprising a series LC resonance circuit and a shunt LC resonance circuit for a mushroom UE.
Demand for connectivity devices is growing at a fast pace, while antenna integration persists as an unsolved “last mile” problem. Small, discrete antennas are commonly made from ceramic dielectric materials in patch or in chip form. Small, discrete antennas can also be made with sheet metal, wire, and can also be printed on Printed Circuit Boards (“PCB”), e.g., as an inverted-F antenna, Planar Inverted-F Antennas (“PIFA”) and the like. The size of such antennas can be reduced by using higher relative permittivity (∈r) materials. However, higher ∈r increases dielectric loss that lowers overall antenna efficiency.
Small antennas also can require a large ground plane and may be very sensitive to nearby objects. In addition, small antennas may be sensitive to the size of the ground plane. Thus, ground plane design can play a significant role in the performance of small antennas. When the size of the ground plane does not meet the antenna's specification, the antenna efficiency can be significantly reduced from 80% to only a few percent or even less. Such small antennas may also have a very short range of only one (1) to two (2) meters.
In contrast, standard ceramic patch antennas offer improved performance. However, their large and thick volumetric nature makes them impractical for increasingly compact devices. Some antenna designs have trimmed their sizes down to 9×9 mm. However, such designs suffer from poor efficiency, gain, and narrow bandwidth. Moreover, miniaturized patch antennas behave like capacitors, needing a large ground plane, thus defeating the goal of miniaturization.
Increasingly small size end-products employ radio “cohabitation”—that is, more than one transmitter and receiver. These designs mix and match of multiple wireless connectivity technologies in one design. Cohabitation can suffer from inadequate receive signal level, high coupling between antennas, and increased signal errors, in addition to undesirable and unintentional interference within the design.
Active integrated electronic antennas with embedded electronic circuits (e.g., LNA, filters, etc.) attempt to mitigate the degradation caused by radio cohabitation. Many active integrated electronic antenna modules are made with a patch antenna(s) on one side of a PCB and the electronic circuits on the other side, shielded with a metal lid. Such antennas can be assembled with a coaxial cable and RF connector for external connection and antenna separation. However, the results are large, bulky, and expensive antenna systems.
Other challenges associated with multiple antennas spaced closely in a small device include strong mutual coupling and cross polarization distortion that result in a distorted radiation pattern(s) and decreased channel capacity. Achieving high isolation between closely-packed antenna elements can be difficult in small devices and impractical in antenna modules.
Mushroom UE can be fabricated as a planar 2-dimensional periodic array of elements, to form a Frequency Selective Surface (“FSS”) or Artificial Magnetic Conductor (“AMC”) based metamaterial. FSS-based or AMC-based metamaterials can be modelled with an equivalent LC circuit similar to the FIG. 5. At higher frequencies such as those in the microwave and radio frequency bands, distribution characteristics of the L & C for the UEs can be engineered to create an Electromagnetic Band Gap (“EBG”) at a defined range of frequencies thereby suppressing surface wave propagation within a prescribed range. These “forbidden operating frequencies” are frequencies at which surface waves generated between the antenna and the ground plane are formed inside the dielectric. Surface waves may be 180° out of phase with the desired radiation of the antenna, and the resulting destructive interference may impair antenna efficiency, gain, and bandwidth.
As an improvement over a conventional metal ground plane, the FSS or AMC surface exhibits EBG characteristics (collectively, EBG surface or EBG ground plane) may be operated as a new type of ground plane for low-profile integration of wire antennas. For example, even when a horizontal wire antenna is extremely close to an EBG surface, the current through the antenna and its image current through the ground plane are in-phase (rather than out-of phase), thereby advantageously strengthening the radiation. The useful bandwidth of an EBG ground plane or surface is generally defined as +90° to −90° phase difference on either side of the central frequency. The structure may be used in applications such as microwave circuits and antennas.
For antenna applications in the Industrial, Scientific and Medical (“ISM”) band of 2.4 GHz an EBG ground plane may be made to cover a frequency range from about 2 GHz to 3 GHz. Typical sizes of the mushroom UE made with microwave grade dielectric material according to the characteristics are shown in Table 1.
TABLE 1MushroomPatch SizeGap (d)Thickness (h)Band-gap(mm)(mm)(mm)(GHz)151.532~3Compare to free0.1 λo0.01 λo0.02 λospace wavelength(⅛ λo)( 1/80 λo)( 1/40 λo)
A need exists to overcome the electric and magnetic limits imposed on System in Package (“SiP”) designers by natural dielectric materials thereby transcending the limitations of the electric and magnetic properties that are inherent in small package designs. UEs as described above may be used to create metamaterials layers suitable for use in SIP designs integrating antennas, power lines, noise suppression filters, radio frequency (“RF”) power splitters, inductors, Surface Acoustic Wave (“SAW”) filters, oscillators, and other electronic circuits more easily, at lower cost, and with increased functionality and reliability. Overcoming the challenges presented by the limitations of electric and magnetic properties of small package designs will lead to the development of active integrated electronic antenna and filter technologies for SiP designers and enable massive participation for the rapid growth of wireless connectivity technologies such as Bluetooth v4.0, Wi-Fi, Near Field Communications, GPS, Ultra-Wide Band (“UWB”), ISM wireless modems, 802.15.4/ZigBee and wireless charging (e.g., Qi/A4WP), and future derivatives of these technologies and standards.